1. Field of the Invention
The invention relates to a process for setting the switching point of a sensor in which, depending on whether the switching point has been exceeded or has not been reached by the sensor signal, an output signal is controlled, and in which the location of the switching point is determined during a calibration process using the values of the sensor signal in the uninfluenced and in the influenced state.
2. Description of Related Art
In known processes (see the SUNX FX-7 Series fiber optic sensor brochure, especially pages 2, 4 & 5), the location of the switching point during the calibration process is set to the average of the values of the sensor signal in the uninfluenced and in the influenced state. This known setting of the location of the switching point is indeed the most common circumstance, but it cannot ensure optimum operating conditions of the sensor.
The described known process for setting the switching point of a sensor is problematical mainly in that the same percentage changes of the sensor signals in the uninfluenced state, i.e., in the state in which the sensor is only minimally influenced by the object to be detected, and in which background signals play an important part, and in the influenced state, i.e., in the state of maximum influence of the object to be detected by the sensor, have different effects on the operating reliability of the sensor. If, for example, the sensor signal in the uninfluenced state is 0.2 V and is 1 V in the influenced state, the switching point is located at 0.6 V according to the described known process for setting the switching point of a sensor. Determination of the switching point according to the described known process, thus, leads to very different operating reserves (stability margin) of the sensor in the influenced and in the uninfluenced state. The concept of operating reserve (BTR) is based on the following definition: EQU BTR(S)=(S-S.sub.SP)/S.sub.SP .multidot.100% (S&gt;S.sub.SP) EQU BTR(S)=(S.sub.SP -S)/S.multidot.100% (S&lt;S.sub.SP)
S=sensor signal PA1 S.sub.SP =switching point
In this example, the operating reserve in the uninfluenced state of the sensor is 200%, while the operating reserve in the influenced state of the sensor is only 66%. This is a disadvantage for the operating reliability of the sensor, since a change of the sensor signal in the influenced state, for example, due to dirty optics of an optical proximity switch, has a greater effect on the operating reliability of the sensor than a change of the sensor signal in the uninfluenced state, for example, based on an increased background signal. Since, generally, the probability of a change of the sensor signal in the uninfluenced state and in the influenced state is roughly the same, this is undesirable.